This invention relates to video display systems and, more particularly, to improvements in the type of video display which employs a deformable reflective surface having deformations that depend upon a stored charge pattern and an optical subsystem for converting the deformations into a viewable image.
There have been previously set forth techniques for displaying video information by storing a charge pattern representative of a video frame in a frame store and utilizing the charge pattern to modify a characteristic of a material. The modified characteristic of the material is then used to obtain a viewable image. For example, in my U.S. Pat. No. 3,882,271 there is disclosed a system called a solid state light modulator wherein a charge pattern on a special array of semiconductor devices is used to obtain deformations of a conductive reflective layer disposed over the array and spaced therefrom by an elastomer material such as silicone gel. An optical subsystem, such as a Schlieren optical system, can then be utilized to convert the pattern of deformations (or "ripples") in the reflective layer into a viewable image. The solid state light modulator is described further in my U.S. Pat. Nos. 4,529,620, 4,626,920, 4,639,788, and 4,641,193.
In my U.S. Pat. Nos. 4,639,788 and 4,641,193 there is disclosed a solid state light modulator which includes an array of columns and rows of devices in a semiconductor substrate. The devices comprise field-effect transistors having spaced doped regions and a gate electrode disposed over an insulating layer that covers the area between the doped regions. A conductive so-called deflection electrode is coupled to one of the doped regions and has a top flat region which extends over its associated device and is spaced therefrom by an insulating material. The deflection electrodes are spaced from the conductive reflective layer by the elastomer, as mentioned above. The desired deformations of the conductive reflective layer are caused by the signals applied to the deflection electrodes. These signals are applied to the appropriate field effect devices, and the devices are switched on at the appropriate times by an addressing system.
In the described system, as set forth in my above-referenced patents, the electrostatic force between each deflection electrode and the overlying portion of the conductive/reflective layer depends upon the voltage difference between the particular deflection electrode and the conductive/reflective layer. This force results in deformation of the conductive/reflective layer which, in turn, is ultimately converted by the optical system into an element of an image. Accordingly, it will be understood that the number of deflection electrodes in the array will determine the grating line spacing of the light modulator and, accordingly, the resolution capability of the system.
One method for increasing the number of deflection electrodes would be to increase the number of elements in the array, but it will be understood that this would increase the cost and difficulty of fabrication. In addition to the obviously greater cost of providing more transistors and associated addressing circuitry, if the packing density of devices is increased, there will be a concomitant increase in the difficulty of designing and fabricating the array.
It is among the objects of the present invention to provide a device, of the general type described, which has improved resolution capability, but does not require a greatly increased number of switching devices in its array or unduly complicate the addressing system.
When making a solid state light modulator of the type described, one of the concerns is the intrusion of light from the imaging system onto the semiconductor devices of the array. The light to be reflected off the conductive/reflective layer of the solid state light modulator is very bright. The conductive/reflective layer cannot be too thick, since it must be deformable. Some of the intense light incident on the conductive/reflective layer is not reflected, and it passes through the conductive/reflective layer and the elastomer layer. Light that strikes certain regions of the semiconductor device can cause spurious switching and/or generation of signals that can degrade or ruin the image to be produced. In my above referenced U.S. Pat. Nos. 4,639,788 and 4,641,193, the deflection electrodes substantially cover their respective semiconductor devices, and provide a degree of protection against the incursion of light. Also, a pattern of isolation electrodes are shown as being disposed between the deflection electrodes.
It is among the additional objects of the present invention to further improve the immunity of the solid state light modulator semiconductor devices against incursion of light from its optical system.